The present invention relates to a high precision spindle with hybrid fluid bearing system and starting/stopping assistant device. It has the advantages of high speed, high precision, low acoustic noise, low power consumption, shorten starting/stopping time and reduced risk of contamination. The spindle is suitable for applications such as hard disk drive, DVD drive, printer and other suitable cases.
With the advance of computer technology, more and more is required of a hard disk drive, optical disk drive, and other motor-driven storage drives. It is expected that data storage capability of a hard disk drive will be much higher with shorter read/write time. Besides the larger storage capacity, the hard disk drive is also expected to have characteristics of lower acoustic noise and better reliability under external shock and vibration. The higher requirements result in each component in hard disk drive to do more and perform better.
There is no exception for a spindle motor. The key task of a spindle motor is to provide a disk drive with turning power that is rotatably stable and reliable for many years. The ideal spindle motor should possess the characteristics of lower repeatable runout (RRO) and non-repeatable runout (NRRO), lower acoustic noise, lower power consumption, fast starting and stopping, and higher resistance to external shock and vibration.
It is difficult for conventional ball bearing spindle motors to meet all of these requirements. Therefore, a conventional ball bearing spindle motor is not likely suitable to be used in next generation of hard disk drive due to its drawbacks of higher non-repeatable runout as well as higher acoustic noise. The drawbacks of ball bearing are caused by the imperfect geometry on the inner race, outer race and balls or rolling elements of ball bearings.
In contrast, fluid film bearings have no surface contact during operation. Hence, it may be a better alternative for ball bearings used in hard disk drives. The fluid film bearing shows significantly lower non-repeatable runout and acoustic noise, and its relative higher damping provides better resistance to external shock and vibration as described in U.S. Pat. No. 5,358,339 to Konno et al., U.S. Pat. No. 5,697,708 to Leuthold et al. and U.S. Pat. No. 5,770,906 to Hazelton et al.
One of the major difficulties with a fluid film bearing in a hard disk drive is leakage of liquid lubricant. The leakage of lubricant degrades the performance of the fluid bearing. Besides, the oil droplets that leaks from the bearing may contaminate the surfaces of disks and cause the failure of the hard disk drive.
In this aspect, the aerodynamic bearing is attractive because there is no risk of lubricant leakage. The spindle motors using aerodynamic bearings are described in U.S. Pat. No. 5,283,491 to Jabbar et al. and U.S. Pat. No. 5,760,509 to Chung et al. However, the air bearings have relatively lower load capacity and stiffness compared with oil bearings at similar geometric conditions. Furthermore, with a pure aerodynamic bearing system, the hub and the base of spindles are electrically insulated during the operation of spindles. The electrical insulation blocks the discharging of static charges from the base of spindles, which would otherwise result in possible damage of magnetoresistence (MR) head and cause failure of hard disk drives.
The air bearings also have relatively higher wear ratio, especially during the starting and stopping times of the spindle motor. Besides, the prior inventions cannot prevent the contamination caused by the tiny particles out of the bearings, which are generated by the wearing of bearing surfaces, especially at the moment of starting and stopping of spindles.
The present invention attempts to overcome the above-mentioned drawbacks in prior inventions and provides a hybrid fluid-bearing system spindle with the advantages of power saving, fast starting, contamination free and cost-effective.
A general objective of the present invention is to provide a power saving, fast starting, contamination free, cost-effective, spindle motor with hybrid fluid bearing system for hard disk drive and other storage devices. The present invention will overcome the limitations and drawbacks of the prior art.
Another objective of the present invention is to provide a spindle motor with magnetic assisting starting/stopping device, which reduces the friction and wearing during the moment of starting/stopping, therefore, results in a fast starting spindle motor with reduced risk of contamination caused by worn particles.
A further objective of the present invention is to provide a hybrid bearing design for disk drive spindles, which comprises hydrodynamic journal bearings and aerodynamic thrust bearings. With the hybrid design of the bearing system, the total power consumption is reduced. By means of ferrofluid seals, the bearing system obtains substantially a contamination free condition.
The basic construction of the hybrid bearing system comprises two hydrodynamic journal bearings and two aerodynamic thrust bearings. The journal bearings are sealed by means of magnetic fluid seals.
An additional objective of the present invention is to provide an electrical path for discharging the static charges in order to protect electric charge sensitive devices, especially for Magnetoresistance (MR) head disk drives.
In one embodiment of the present invention, the aforementioned hybrid bearing unit is assembled to a disk drive spindle. The spindle comprises a rotational hub assembly and a stationary base assembly. The hub assembly consists of a hub onto which the magnetic recording disks can be mounted, a shaft sleeve housing that is securely fixed to the hub, two magnetic ring and two sealing rings that are fixed to the upper and bottom ends of the shaft sleeve housing, a shaft sleeve, two thrust bearing covers, rotor of an electric motor, e.g. magnetic poles and their back iron. The base assembly consists of a base, an electric motor stator, a shaft that is fixed to the base, a thrust plate that is also fixed to the base, a magnetic starting/stopping device that is located beneath the lower cover of thrust bearing, respectively.
The invention will be described in details with reference to the drawings.